A drought is a prolonged period of abnormally low rainfall, which leads to a shortage of water. Wildfires, also known as forest fires or bushfires, are uncontrolled fires that burn in wildland areas, consuming combustible vegetation. This article explores the scientific connection between droughts and wildfires.
Drought’s Role in Wildfire Readiness
Drought conditions significantly contribute to the environmental circumstances that make landscapes susceptible to wildfires. A deficiency of precipitation over an extended period results in reduced soil moisture, leading to widespread drying of the environment.
Lower atmospheric humidity, often accompanying drought, further exacerbates these dry conditions. This lack of atmospheric moisture draws water from plants and the ground, increasing aridity. Elevated temperatures, often associated with drought, also increase evapotranspiration, the process of water evaporating from land and transpiring from plants. These combined factors create a drier environment that is more prone to ignition and rapid fire spread.
Vegetation as Fuel
Drought transforms vegetation into highly flammable material, effectively creating abundant fuel for wildfires. As soil moisture decreases, both living vegetation, such as trees and shrubs, and dead vegetation, like leaf litter and fallen branches, begin to dry out. This reduction in water content within plants makes them more volatile and easier to ignite.
The physiological stress from drought can lead to leaf shedding and, in severe cases, tree mortality, converting live fuels into dead fuels. Dead fuels have significantly lower moisture content than live fuels, making them readily available to burn. This accumulation of dry, dead plant material provides a continuous and easily ignitable fuel bed, allowing fires to spread rapidly and intensely across the landscape.
Other Drivers of Wildfire
While drought creates conditions conducive to wildfires, other factors are necessary for ignition and spread. Wildfires can be ignited by natural causes, such as lightning strikes, which are a primary natural source of ignition, particularly during dry seasons. Volcanic eruptions and spontaneous combustion are also natural ignition sources.
Human activities cause nearly 85% of wildland fires in the United States. These include unattended campfires, discarded cigarettes, equipment malfunctions, and debris burning. Wind is another factor that can accelerate wildfire spread by providing additional oxygen and carrying embers to ignite new fires, even across large distances. Topography, such as slopes and valleys, influences fire behavior, as fires often spread more rapidly uphill due to preheating of fuels.
Consequences of Drought-Fueled Wildfires
Wildfires occurring in drought-stricken areas can lead to widespread and long-lasting consequences. Ecologically, these fires cause habitat destruction and can lead to significant soil erosion, as the protective vegetation layer is removed. The intense heat can alter soil properties, impacting water absorption and nutrient cycles, which then affects water quality in nearby streams and rivers.
Air quality degrades substantially due to smoke, which contains fine particulate matter and gases that can travel long distances. This smoke poses threats to human health, contributing to respiratory and cardiovascular issues. Furthermore, drought-fueled wildfires can threaten human infrastructure, destroying homes, businesses, and essential utilities, particularly in areas where wildlands meet urban development. There is also a feedback loop where severe wildfires can exacerbate drought conditions by damaging vegetation and reducing soil moisture retention, further altering local climates.